BACKGROUND
[0001] Silicon pressure sensors offer multiple benefits that include small size, good quality,
and stable performance. Further, since multiple identical sensors can be fabricated
simultaneously on a single wafer, silicon pressure sensors are also cost effective
to manufacture. In at least one example of a pressure sensor, piezo-resistors are
fabricated on a silicon diaphragm such that the piezo-resistors sense the strain in
the diaphragm as the diaphragm reacts to pressure applied by the pressure media. Even
when the pressure media is clean dry air, the silicon sensing die requires some form
of isolation from the environment. For absolute sensors this is provided by the normal
SiO2 layer that is formed. The clean dry air is contained to only contact the side
of the diaphragm that does not contain metal traces and pads. That surface is exposed
only to a reference vacuum. For precision applications where the pressure media is
limited to air, the silicon diaphragm can be mounted on a stress isolation member.
A similar pressure electric transducer is disclosed in the patent application
US 4 085 620.
[0002] In one example, the stress isolation member is a Pyrex tube. The Pyrex tube surface
is hygroscopic in nature and absorbs H
2O from the pressure media over time. This change in water content alters the tube
geometry slightly, which cause the sensing element to drift. In addition to long term
drift due to differences in the coefficient of expansion of silicon and Pyrex, and
due to stresses produced during assembly processes, the pressure sensors need extensive
conditioning to remove early drift components. Finally, unwanted leakage currents
between the piezo-resistors and the housing of the sensor or external electrical connection
can occur. The thin coating of silicon oxide that naturally forms is often relied
on to provide electrical isolation. This film also can absorb water, which also may
produce sensor drift.
SUMMARY
[0003] The present invention is defined by the appended claims.
[0004] In one embodiment a pressure sensor according to claim 1 is provided. The pressure
sensor includes a housing comprising an input port configured to allow a media to
enter the interior of the housing when the housing is placed in an environment containing
the media. A support is mounted within the housing, the support defining a first aperture
extending therethrough. A stress isolation member is mounted within the first aperture
of the support, the stress isolation member defining a second aperture extending therethrough,
wherein the stress isolation member is composed of silicon. The sensor die includes
a silicon substrate having an insulator layer on a first side of the silicon substrate;
and sensing circuitry disposed in the insulator layer on the first side, wherein a
second side of the silicon substrate is exposed to the second aperture of the stress
isolation member and the second side is reverse of the first side.
DRAWINGS
[0005] Understanding that the drawings depict only exemplary embodiments and are not therefore
to be considered limiting in scope, the exemplary embodiments will be described with
additional specificity and detail through the use of the accompanying drawings, in
which:
Figure 1 is a diagram illustrating a cross-sectional view of a pressure sensing device
having a integrated silicon-on-insulator (SOI) sensor and a silicon stress isolation
member according to an embodiment described in the present disclosure;
Figure 2 is a diagram illustrating an exploded perspective view of a sensor die, stress
isolation member, and support of the pressure sensing device of Figure 1 according
to an embodiment described in the present disclosure; and
Figure 3 is a flow diagram illustrating a method for fabricating the pressure sensing
device of Figure 1 according to an embodiment described in the present disclosure.
[0006] In accordance with common practice, the various described features are not drawn
to scale but are drawn to emphasize specific features relevant to the exemplary embodiments.
DETAILED DESCRIPTION
[0007] In the following detailed description, reference is made to the accompanying drawings
that form a part hereof, and in which is shown by way of illustration specific illustrative
embodiments.
[0008] In at least one embodiment, a sensor die functioning as a diaphragm may be mounted
on the stress isolation member (pedestal) that defines a first aperture extending
through a stress isolation member so that a pressure media can pass through the aperture
and exert pressure on the diaphragm. The sensor die can be composed of a silicon on
insulator substrate and a stress isolation member can be composed of silicon such
that the sensor die and the stress isolation member can have substantially equal coefficients
of thermal expansion. This can also enable the sensor die and the stress isolation
member to be fabricated at the wafer level.
[0009] In further embodiments, the sensor die and the stress isolation member can be mounted
within a second aperture of a support, where the second aperture extends through the
support. The support can be mounted to a housing of the pressure sensor and can provide
electrical connection and a pressure port for the sensor die.
[0010] In still further embodiments, moisture absorption, due to hygroscopic materials of
the pressure sensor device, is avoided by coating surfaces of such materials that
are exposed to the pressure media with a protective layer through atomic layer deposition.
To prevent the surfaces of the support, stress isolation member, and the sensor die
from absorbing moisture in a pressure media, some or all of these surfaces that are
exposed to the pressure media can be coated with a protective layer through an atomic
layer deposition process.
[0011] An example pressure sensing device 100 is now described with respect to Figures 1
and 2. Figure 1 is a cross-section view of a pressure sensing device 100 and Figure
2 is an exploded perspective view of a portion of the pressure sensing device 100.
The pressure sensing device 100 is capable of measuring the pressure in certain media.
For example, the pressure media sensed by the pressure sensing device 100 may include
air or a liquid. To sense the pressure of the pressure media, the pressure sensing
device 100 includes an input port 102, wherein the input port 102 allows the pressure
media to enter a housing 104. The housing 104 protects the pressure sensing device
100 from environmental influences that can damage the pressure sensing device 100
or affect the performance of the pressure sensing device 100.
[0012] To sense the pressure of the pressure media inside the housing 104, the pressure
sensing device 100 includes a sensor die 106. In at least one implementation, the
sensor die 106 is a piezo-resistive silicon pressure sensing die, where piezo-resistors
formed on a first side 105 of the sensor die 106, respond to strain in the sensor
die 106. The sensor die 106 includes a silicon diaphragm with sensor circuitry, such
as the piezo-resistors, formed on the diaphragm. The piezo-resistors change resistance
in accordance with movement of the diaphragm.
[0013] In an embodiment, the sensor die 106 comprises a silicon-on-insulator (SOI) substrate
having the sensing circuitry fabricated thereon. In particular, the sensor die 106
is composed of a silicon substrate having an insulator layer on the first side 105
thereof. The insulator layer can be formed on the silicon substrate in any suitable
manner such as by epitaxial growth. The sensing circuitry is fabricated in the insulator
layer on the first side 105 of the silicon substrate. Accordingly, the insulator layer
has a thickness sufficient to enable fabrication of piezo-resistors therein. The sensor
die 106 also has a second side 107 that is reverse of the first side 105. After fabrication
of the sensor die 106, the second side 107 may naturally form a thin silicon oxide
layer upon exposure to air or other media.
[0014] Stress to the housing 104 may affect the components of the pressure sensing device
100 that are located within the housing 104. While some of the components within the
housing are minimally affected by stress, strain on the piezo-resistor located on
the sensor die 106, caused by stress on the housing 104, can negatively affect the
accuracy of pressure measurements made by the pressure sensing device 100. For example,
strain on the housing 104 may strain the sensor die 106 in a way that is similar to
the strain applied to the diaphragm of the sensor die 106 by a pressure media, which
leads to bias in pressure measurements derived from the sensor die 106. In certain
implementations, to isolate the sensor die 106 from stress on the housing 104 or other
components in the sensing device 100, the sensor die 106 is mounted on a stress isolation
member 110. The stress isolation member 110 isolates the sensor die 106 from strain
applied on the housing 104 or caused by other components within the housing 104.
[0015] In certain embodiments, the stress isolation member 110 is composed of silicon. In
particular, the stress isolation member 110 can be composed of a silicon substrate
having an aperture 108 defined therein. The aperture 108 extends all the way through
the silicon substrate. The stress isolation member 110 is mounted to the second side
107 of the sensor die 106 such that the aperture 108 extends from and is open to the
second side 107 of the sensor die 106 on one end and is open to pressure media on
the other end. The stress isolation member 110 is also referred to as a pedestal.
The stress isolation member 110 extends away from the second side 107 of the sensor
die 106. In an example, the sensor die 106 is mounted to a first end of the stress
isolation member 110 and the support 122 is mounted proximate a second end 114 of
the stress isolation member 110, wherein the second end 114 is reverse of the first
end.
[0016] In at least one embodiment, to expose the sensor die 106 to the pressure media, the
pressure media enters the housing 104 through the input port 102 and then passes through
the aperture 108 in the stress isolation member 110. The pressure media within the
aperture 108 applies a force against the sensor die 106, which force causes the piezo-resistors
to strain as a diaphragm in the sensor die 106 moves in accordance with the pressure
applied by the pressure media. The strain on the piezo-resistor changes the resistance
of piezo-resistors in the piezo-resistor. As a known current passes through the piezo-resistor,
the voltage drop due to the resistance of the piezo-resistors may be used to determine
the pressure of the pressure media against the diaphragm of the sensor die 106. In
at least one embodiment, the piezo-resistors include both pressure sensing elements
and temperature sensing elements.
[0017] As also shown in Figure 2, in some embodiments, the sensor die 106 and the stress
isolation member 110 have substantially the same cross-sectional dimensions when viewed
with the sensor die 106 proximate the viewer and the stress isolation member 110 extending
away from the viewer. In such embodiments, the cross-sectional size of the sensor
die 106 and the stress isolation member 110 is limited by the sensor die 106 and not
the stress isolation member 110. Accordingly, the overall cross-section can be maintained
small. In an example, both the sensor die 106 and the stress isolation member 110
have rectangular (e.g., square) cross-sections.
[0018] Advantageously, with the stress isolation member 110 composed of the same material
(silicon) as the sensor die 106, the stress isolation member 110 and the sensor die
106 can achieve substantially the same coefficient of thermal expansion. Thus, when
the stress isolation member 110 and/or sensor die 106 experience thermal expansion,
the stress isolation member 110 and the sensor die 106 expand at the same rate to
reduce the stress applied to the piezo-resistors formed on the sensor die 106 due
to thermal expansion. In an example, the crystalline orientation of the stress isolation
member 110 and of the sensor die 106 are aligned in order to further match the coefficients
of thermal expansion.
[0019] The sensor die 106 is bonded to the stress isolation member 110 using a low temperature
diffusion process. In such a process, surface activation of the silicon surface allows
the low temperature silicon to silicon, surface to surface bonding. Such low temperature
bonding can be at or below 600 degress Celsius and, in a particular example is around
400-450 degrees Celsius.
[0020] In an example, the stress isolation member 110 has a generally rectangular cuboid
shape with the aperture 108 extending therethrough. In an implementation of such an
example, the aperture 108 extends longitudinally through the long dimension of the
rectangular cuboid shape. In an example, the long dimension of the rectangular cuboid
shape is around 0.156 inches in length, which is substantially longer than the thickness
of the sensor die 106.
[0021] In certain embodiments, the second side 107 of the sensor die 106 is exposed to the
pressure media in the aperture 108 and an opposite side of the sensor die 106 is exposed
to a reference chamber 121. The reference chamber 121 is a sealed environment having
a known pressure. In an example, the reference chamber 121 is maintained as a vacuum.
The housing 104 can be sealed to maintain the pressure in the reference chamber 121.
The sensing circuitry on the first side 105 of the sensor die 106 can be electrically
coupled to components and/or connections on the housing 104 or other electronics associated
with the housing 104. Accordingly, the signals from the piezo-resistors on the sensor
die 106 are sent through wires that are bonded to the first surface 105 of the sensor
die 106 within the reference chamber 121, where the wires extend directly from the
sensor die 106 to the further electronics such as front end circuitry. The front end
circuitry includes electronics that, in part, function to control the input to the
electrical elements on the sensor die 106. For example, the front end circuitry includes
analog to digital converters, digital to analog converters, multi chip modules and
the like. In at least one implementation, the front end circuitry performs functionalities
such as pressure output characterization, output signal conditioning, and the like.
[0022] In certain embodiments, the front end circuitry is electrically connected to an electrical
connector that is welded to the housing 104 with a hermetic weld. The electrical connector
extends from the housing 104 and connects to an external system. The electrical connector
can be threaded to aid in the integration of the pressure sensing device 100 in a
larger system. Thus, through the electrical connector, an external system is able
to acquire pressure measurements from the piezo-resistors on the sensor die 106.
[0023] In an example, a getter may be placed within the reference chamber 121. The getter
can be activated according to methods known to those having skill in the art. The
getter can absorb any remnant gaseous molecules present in the reference chamber 121
after bonding and absorbs molecules that are out gassed from elements in the reference
chamber 121 after bonding.
[0024] In at least one implementation, when the sensor die 106 is mounted on the stress
isolation member 110, the stress isolation member 110 is mounted to a support 122.
In certain exemplary implementations, the support 122 is composed of a ceramic, such
as an alumina blank, or other brazeable material having a coefficient of thermal expansion
similar to silicon. The stress isolation member 110 can be mounted to the support
122 using a braze 116. The support 122 includes an aperture 112 into which the stress
isolation member 110 is mounted. The aperture 112 has a cross-section and size that
corresponds to an outer cross-section of the stress isolation member 110, such that
the stress isolation member 110 can be inserted therein. In the example shown in Figures
1 and 2, the aperture 112 and the outer cross-section of the stress isolation member
110 are rectangular. Accordingly, the outer surface of the stress isolation member
110 is attached to the inner surface of the support 122, for example, with a braze
116. The support 122 is attached to the housing 104 to provide the mechanical coupling
between the sensor die 106 and stress isolation member 110 assembly and the housing
104. Portions of the outer surface of the support 122 can be mounted to the housing
104. In an example, the support 122 is bonded to the housing 104 through a braze 118.
Alternatively, the stress isolation member 110 and the substrate 122 are bonded to
the housing through a solder joint.
[0025] When a stress isolation member 110 is manufactured from silicon, and when the silicon
material interacts with air in the pressure media, a layer of hygroscopic silicon
dioxide forms. The silicon dioxide can absorb moisture out the air and causes the
stress isolation member 210 to change shape. The stress isolation member 110 may expand
in such a way that the piezo-resistors on the sensor die 106 become strained, thus
causing a bias in the measurements produced by the piezo-resistors. In certain embodiments,
the stress isolation member 110 is protected from moisture by an atomic layer deposition
(ALD) coating 126 that prevents the moisture in the pressure media from contacting
the stress isolation member 110. For example, the ALD coating 126 includes a coating
of metal oxide that is deposited on the surfaces of the stress isolation member 110
and the substrate 122 that are exposed to the pressure media. In at least one embodiment,
the coating 226 is a metal oxide such as alumina or titanium oxide. In particular,
these surfaces include the interior surfaces of the aperture 108. Other surfaces can
also be included such as an end face 114 of the stress isolation member 110. In one
exemplary implementation, the ALD coating 126 is applied before the stress isolation
member 110 and the substrate 122 are mounted within the housing 104. Alternatively,
the ALD coating 126 is applied after the stress isolation member 110 and the substrate
122 are mounted within the housing 104. In some examples, the ALD coating 126 can
be placed on the portion of the second surface 107 of the sensor die 106 that is exposed
within the aperture 108 of the stress isolation member 110. Moreover, in the some
examples, the ALD coating is placed on surfaces of the support 122 that are exposed
to pressure media.
[0026] Advantageously, the SOI geometry of the sensor die 106 can provide a secondary isolation
for any leakage paths through the ALD coating. The SOI geometry can also allow the
pressure sensor to be operated at temperatures above 125 degrees Celcius, where reverse
bias diode leakage currents can become problematic.
[0027] Figure 3 is a flow diagram of one exemplary embodiment of a method 300 for fabricating
the pressure sensor 100. Advantageously, since the sensor die 106 and the stress isolation
member 110 are composed of silicon, the sensor die 106 and the stress isolation member
110 can be fabricated and bonded together at the wafer level, where multiple sensor
dies 106 and stress isolation members 110 are fabricated simultaneously.
[0028] Sensor dies 106 can be formed by fabricating multiple sets of piezo-resistors are
fabricated in an insulator layer of a silicon-on-insulator (SOI) wafer (302). The
SOI wafer corresponds to the substrate of multiple sensor dies 106, and the insulator
layer corresponds to the first side 105 of the sensor die 106. The insulator layer
of the SOI wafer can be formed in any suitable manner such as by epitaxial growth
of on a silicon substrate. In such an example, the insulator layer is grown thick
enough to be used for forming piezo-resistors. Each set of piezo-resistors corresponds
to the piezo-resistors for sensing circuitry of a single sensor die 106. The sets
of piezo-resistors can be positioned on the SOI wafer using any suitable wafer level
plan. To fabricate the piezo-resistors, the insulator layer is appropriately doped
and etched to form the piezo-resistor structures. An etch is also performed to form
a cavity for each sensing circuitry, the cavity for use by a diaphragm. Once the piezo-resistors
and cavities are formed, the diffusion surface of the SOI wafer is polished flat.
In an example, metalized paths and pads are not applied at this time.
[0029] A plurality of through holes (apertures 108) can be etched in a second silicon wafer
to form a plurality of stress isolation members 110 (304). Each aperture 108 can extend
all the way through the silicon wafer and can correspond to the aperture 108 extending
through a stress isolation member 110. The apertures 108 can be positioned on the
silicon wafer in a manner that corresponds to the positioning of the sets of piezo-resistors
on the SOI wafer, and in a particular example to the position of the cavity for the
diaphragm of each sensing circuitry, such that each aperture 108 matches up with a
set of piezo-resistors and, in particular, a diaphragm. The silicon wafer can be selected
as a wafer having the same crystalline orientation as the SOI wafer.
[0030] Once the piezo-resistors are fabricated in the SOI wafer and the through holes are
etched in the silicon wafer, the SOI wafer and the silicon wafer can be bonded together
(306). The silicon wafer is bonded to the side of the SOI wafer reverse of the insulator
layer; the side that is reverse of the insulator layer corresponds to the second side
107 of the sensor die 106. Bonding the SOI wafer to the silicon wafer includes aligning
the apertures 108 in the silicon wafer with the sets of piezo-resistors and/or cavities
for diaphragms. For example, each aperture 108 can be aligned with a cavity for a
diaphragm and/or aligned with a set of piezo-resistors. Since the silicon wafer is
bonded to the side of the SOI wafer that is reverse of the insulator layer, the apertures
108 are aligned piezo-resistors and/or cavities while being disposed proximate this
second side 107. The silicon wafer is then bonded to the SOI wafer in this alignment.
That is, the apertures 108 are aligned with the reverse side of the piezo-resistors
and/or cavities. In an example, the silicon wafer is also bonded to the SOI wafer
such that the crystalline orientation of the silicon wafer is aligned with the crystalline
orientation of the SOI wafer, as mentioned above. The silicon wafer and the SOI wafer
can be bonded together using a low temperature using a low temperature diffusion process.
In such a process, surface activation of the side of the SOI wafer that is reverse
of the insulator layer and surface activation of a surface of the silicon wafer allows
the low temperature silicon to silicon, surface to surface bonding. Such low temperature
bonding can be at or below 600 degress Celsius and, in a particular example is around
400 or 450 degrees Celsius.
[0031] Metal traces and wire bonding pads are then fabricated on the insulator layer of
the combined SOI wafer and silicon wafer (308). The metal traces can effectuate appropriate
connections in each set of piezo-resistors to one another and to the wire bonding
pads.
[0032] The combined SOI wafer and silicon wafer are then singulated (e.g., sawed) to form
multiple discrete pressure sensor primitives (310), each pressure sensor primitive
including a sensor die 106 (a singulated portion of the SOI wafer) bonded to a stress
isolation member 110 (a corresponding singulated portion of the silicon wafer).
[0033] A pressure sensor primitive is then mounted to a support 122 having an aperture 112
therein (312). In an example, the pressure sensor primitive is mounted to a support
122 by brazing the external surface of the stress isolation member 110 to an internal
surface of the aperture 112 of the support 122. This braze 116 is vacuum tight. In
an example, the sensor die 106 is mounted to a first end of the stress isolation member
110 and the support 122 is mounted proximate a second end 114 of the stress isolation
member 110, wherein the second end 114 reverse of the first end.
[0034] The pressure sensor primitive mounted to the support 122 is then mounted within the
housing 104 (314). For example, the pressure sensor primitive and support 122 are
placed within a housing 104 having an input port 102 such that pressure media entering
the input port 102 is able to enter the opening of the aperture 108 on the stress
isolation member 110. In at least one exemplary embodiment, the pressures sensor primitive
with the support 122 can be mounted into the housing 104 by attaching the support
122 to the housing 104 using a braze 118. This braze 118 is vacuum tight.
[0035] The sensing circuitry on the sensor die 106 can be electrically connected to components
on the housing 104, such as front end circuitry (316). For example, pads on the sensor
die 106 can be wire bonded to the components to electrically connect the sensing circuitry
on the sensor die 106 to the wire bonds.
[0036] The area around the reference chamber 121 in the housing 104 is then sealed to form
the reference chamber 121 (318). Finally, the pressure sensor is conditioned to remove
the tendency for the sensor measurement to drift over time (320).
1. A pressure sensor (100) comprising:
a housing (104) comprising an input port (102) configured to allow a media to enter
the interior of the housing (104) when the housing (104) is placed in an environment
containing the media;
a support (122) mounted within the housing (104), the support (122) defining a first
aperture (112) having a uniform cross section extending through the support, and wherein
the support is composed of an insulating material having a coefficient of thermal
expansion similar to silicon;
a stress isolation member (110) mounted within the first aperture (112) of the support
(122), the stress isolation member (110) having a rectangular cuboid shape and defining
a second aperture (108) extending longitudinally through the rectangular cuboid shape,
wherein the stress isolation member (110) is composed of silicon, and wherein the
cross-section of the first aperture matches an outer cross section of the stress isolation
member; and
a sensor die (106) bonded to the stress isolation member (110), the sensor die (106)
including:
a silicon substrate having an insulator layer on a first side (105) of the silicon
substrate; and
sensing circuitry disposed in the insulator layer on the first side (105), wherein
a second side (107) of the silicon substrate is exposed to the second aperture (108)
of the stress isolation member (110) and the second side (107) is reverse of the first
side (105); and wherein the second side of the silicon substrate is bonded to a first
surface of the stress isolation member to form a silicon to silicon bond between the
sensor die and the stress isolation member,
wherein the stress isolation member (110) extends away from the second side (107)
of the silicon substrate, the sensor die (106) being mounted to a first end of the
stress isolation member (110), wherein the support (122) is mounted proximate a second
end (114) of the stress isolation member (110), wherein the second end (114) is reverse
of the first end.
2. The pressure sensor (100) of claim 1, wherein the support (122) is fabricated from
a ceramic
3. The pressure sensor (100) of claim 1 or 2, further comprising an atomic layer deposition
coating (126) that covers an interior surface of the stress isolation member (110)
and the second side (107) of the silicon substrate which are exposed to the media.
4. The pressure sensor (100) of claim 3, wherein the atomic layer deposition coating
(126) covers a portion of the support (122).
5. The pressure sensor (100) of any of claims 1 to 4, wherein the support (122) and the
stress isolation member (110) are mounted together using a braze (116).
6. The pressure sensor (110) of any of claims 1 to 5, wherein a crystalline orientation
of the stress isolation member (110) is aligned with a crystalline orientation of
the sensor die (106).
7. A method (300) for fabricating a pressure sensor, the method comprising:
fabricating multiple sets of piezo-resistors (302) in an insulator layer of a first
silicon wafer, wherein each set of piezo-resistors corresponds to sensing circuitry
for a sensor die;
etching a plurality of through holes (304) in a second silicon wafer, wherein each
through hole corresponds to a first aperture for a stress isolation member;
bonding the second silicon wafer (306) to a side of the first silicon wafer reverse
of the insulator layer using a low temperature silicon-to-silicon, surface-to-surface,
diffusion process, wherein bonding includes aligning the second silicon wafer with
the first silicon wafer such that each through hole is reverse of a set of piezo -resistors;
dicing the bonded first and second silicon wafers (310) to form a plurality of discrete
pressure sensor primitives, each pressure sensor primitive including:
a sensor die bonded to a stress isolation member, the sensor die composed of a portion
of the first silicon wafer including a set of piezo-resistors; and
the stress isolation member composed of a portion of the second silicon wafer, the
stress isolation member having a rectangular cuboid shape and defining the first aperture
(108) extending longitudinally through the rectangular cuboid shape;
providing a plurality of supports, each support defining a second aperture having
a uniform cross-section extending through the support, and wherein the cross-section
of the second aperture that matches an outer cross section of the stress isolation
member;
mounting each pressure sensor primitive to a support (312) such that a portion of
the outer surface of each stress isolation member is attached to the inner surface
of the second aperture of a corresponding support, wherein mounting each pressure
sensor primitive to a support includes brazing the pressure sensor device to the support,
wherein each pressure sensor primitive is mounted such that the support is brazed
to the stress isolation member proximate an end of the stress isolation member that
is reverse of an end in which the sensor die is mounted;
mounting the stress isolation member of a pressure sensor primitive to a housing (314);
coating surfaces of the stress isolation member and the sensor die that will be exposed
to media with an atomic layer deposition of a metal oxide; and
sealing the housing (318) such that the side of the sensor die having the sensing
circuitry is within an environment having a known pressure and is hermetically isolated
from the second aperture of the stress isolation member.
8. The method of claim 7, comprising:
after bonding the second silicon wafer to the first silicon wafer, fabricating metal
traces and wire bonding pads (308) on a side of the first silicon wafer having the
insulator layer to form sensing circuitry.
9. The method of any of claims 7 or 8, wherein bonding includes bonding at lower than
600 degrees Celcius.
10. The pressure sensor (100) of any of claims 1 to 6, wherein the stress isolation member
(110) has the same cross-sectional dimensions as the sensor die (106).
1. Drucksensor (100), umfassend:
ein Gehäuse (104), das einen Eingangsanschluss (102) umfasst, der konfiguriert ist,
um einem Medium zu erlauben, in den Innenraum des Gehäuses (104) einzutreten, wenn
das Gehäuse (104) in einer Umgebung angebracht wird, die das Medium enthält;
einen Träger (122), der in dem Gehäuse (104) montiert ist, wobei der Träger (122)
eine erste Öffnung (112) definiert, die einen gleichförmigen Querschnitt aufweist
und die sich durch den Träger erstreckt; und wobei der Träger aus einem isolierenden
Material besteht, das einen Wärmeausdehnungskoeffizienten aufweist, der ähnlich wie
der von Silizium ist;
ein Belastungsisolierungselement (110), das in die erste Öffnung (112) des Trägers
(122) montiert ist, wobei das Belastungsisolierungselement (110) eine rechteckige
Quaderform aufweist und eine zweite Öffnung (108) definiert, die sich in Längsrichtung
durch die rechteckige Quaderform erstreckt, wobei das Belastungsisolierungselement
(110) aus Silizium besteht, und wobei der Querschnitt der ersten Öffnung mit einem
Außenquerschnitt des Belastungsisolierungselements übereinstimmt; und
einen Sensorchip (106), der an das Belastungsisolierungselement (110) gebondet ist,
wobei der Sensorchip (106) aufweist:
ein Siliziumsubstrat, das eine Isolatorschicht auf einer ersten Seite (105) des Siliziumsubstrats
aufweist; und
eine Sensorschaltung, die in der Isolatorschicht auf der ersten Seite (105) angebracht
ist, wobei eine zweite Seite (107) des Siliziumsubstrats zur zweiten Öffnung (108)
des Belastungsisolierungselements (110) freigelegt ist, und wobei sich die zweite
Seite (107) entgegengesetzt zur ersten Seite (105) befindet; und
wobei die zweite Seite des Siliziumsubstrats an eine erste Oberfläche des Belastungsisolierungselement
gebondet wird, um einen Silizium-auf-Silizium-Bond zwischen dem Sensorchip und dem
Belastungsisolierungselement zu bilden,
wobei sich das Belastungsisolierungselement (110) von der zweiten Seite (107) des
Siliziumsubstrats weg erstreckt, wobei der Sensorchip (106) an das erste Ende des
Belastungsisolierungselements (110) montiert ist, wobei der Träger (122) in der Nähe
eines zweiten Endes (114) des Belastungsisolierungselements (110) montiert ist, wobei
sich das zweite Ende (114) entgegengesetzt zum ersten Ende befindet.
2. Drucksensor (100) nach Anspruch 1, wobei der Träger (122) aus einem Keramikmaterial
hergestellt ist.
3. Drucksensor (100) nach Anspruch 1 oder 2, der außerdem eine Beschichtung aus einer
Atomlagenabscheidung (126) umfasst, die eine Innenfläche des Belastungsisolierungselements
(110) und die zweite Seite (107) des Siliziumsubstrats bedeckt, die dem Medium ausgesetzt
sind.
4. Drucksensor (100) nach Anspruch 3, wobei die Beschichtung der Atomlagenabscheidung
(126) einen Teil des Trägers (122) bedeckt.
5. Drucksensor (100) nach einem der Ansprüche 1 bis 4, wobei der Träger (122) und das
Belastungsisolierungselement (110) mithilfe einer Hartlötung (116) aneinander montiert
sind.
6. Drucksensor (110) nach einem der Ansprüche 1 bis 5, wobei eine Kristallorientierung
des Belastungsisolierungselements (110) auf eine Kristallorientierung des Sensorchips
(106) ausgerichtet ist.
7. Verfahren (300) zum Herstellen eines Drucksensors, wobei das Verfahren umfasst:
Herstellen von mehreren Gruppen von Piezowiderständen (302) in einer Isolatorschicht
eines ersten Siliziumwafers, wobei jede Gruppe von Piezowiderständen einer Sensorschaltung
für einen Sensorchip entspricht;
Ätzen einer Vielzahl von Durchgangsöffnungen (304) in einen zweiten Siliziumwafer,
wobei jede Durchgangsöffnung einer ersten Öffnung für ein Belastungsisolierungselement
entspricht;
Bonden des zweiten Siliziumwafers (306) auf eine Seite des ersten Siliziumwafers entgegensetzt
zur Isolatorschicht mithilfe eines Niedrigtemperatur-Diffusionsprozesses von Silizium-auf-Silizium
und Oberfläche-auf-Oberfläche, wobei das Bonden ein Ausrichten des zweiten Siliziumwafers
auf den ersten Siliziumwafer umfasst, sodass sich jede Durchgangsöffnung entgegengesetzt
zu einer Gruppe von Piezowiderständen befindet;
Vereinzeln der gebondeten ersten und zweiten Siliziumwafer (310), um eine Vielzahl
von diskreten Drucksensorrohlingen zu bilden, wobei jeder Drucksensorrohling aufweist:
einen Sensorchip, der an ein Belastungsisolierungselement gebondet ist, wobei der
Sensorchip aus einem Teil des ersten Siliziumwafers besteht, der eine Gruppe von Piezowiderständen
aufweist; und
das Belastungsisolierungselement, das aus einem Teil des zweiten Siliziumwafers besteht,
wobei das Belastungsisolierungselement eine rechteckige Quaderform aufweist und die
erste Öffnung (108) definiert, die sich in Längsrichtung durch die rechteckige Quaderform
erstreckt;
Bereitstellen einer Vielzahl von Trägern, wobei jeder Träger eine zweite Öffnung definiert,
die einen gleichförmigen Querschnitt aufweist und die sich durch dem Träger erstreckt,
und wobei der Querschnitt der zweiten Öffnung mit einem Außenquerschnitt des Belastungsisolierungselements
übereinstimmt;
Montieren jedes Drucksensorrohlings an einen Träger (312), sodass ein Teil der Außenfläche
von jedem Belastungsisolierungselement an der Innenfläche der zweiten Öffnung eines
entsprechenden Trägers befestigt wird, wobei das Montieren von jedem Drucksensorrohling
an einen Träger ein Hartlöten der Drucksensorvorrichtung an den Träger umfasst, wobei
jeder Drucksensorrohling so montiert wird, dass der Träger in der Nähe eines Endes
des Belastungsisolierungselements, das sich entgegengesetzt zu einem Ende befindet,
in das der Sensorchip montiert ist, an das Belastungsisolierungselement hartgelötet
wird;
Montieren des Belastungsisolierungselements eines Drucksensorrohlings an ein Gehäuse
(314);
Beschichten von Oberflächen des Belastungsisolierungselements und des Sensorchips,
die den Medien ausgesetzt werden, mit einer Atomlagenabscheidung eines Metalloxids;
und
Abdichten des Gehäuses (318), sodass die Seite des Sensorchips, welche die Sensorschaltung
aufweist, in einer Umgebung liegt, die einen bekannten Druck aufweist und hermetisch
von der zweiten Öffnung des Belastungsisolierungselements abgedichtet ist.
8. Verfahren nach Anspruch 7, das umfasst:
nach dem Bonden des zweiten Siliziumwafers an den ersten Siliziumwafer, Herstellen
von Metallleiterbahnen und Drahtbondflächen (308) auf einer Seite des ersten Siliziumwafers,
der die Isolatorschicht aufweist, um die Sensorschaltung zu bilden.
9. Verfahren nach einem der Ansprüche 7 oder 8, wobei das Bonden ein Bonden bei weniger
als 600 Grad Celsius umfasst.
10. Drucksensor (100) nach einem der Ansprüche 1 bis 6, wobei das Belastungsisolierungselement
(110) die gleichen Querschnittsabmessungen wie der Sensorchip (106) aufweist.
1. Capteur (100) de pression comportant :
un boîtier (104) comportant un orifice (102) d'entrée configuré pour permettre à un
milieu de pénétrer à l'intérieur du boîtier (104) lorsque le boîtier (104) est placé
dans un environnement contenant le milieu ;
un support (122) monté à l'intérieur du boîtier (104), le support (122) définissant
une première ouverture (112) présentant une section droite uniforme s'étendant à travers
le support, et le support étant composé d'un matériau isolant présentant un coefficient
de dilatation thermique similaire à celui du silicium ;
un élément (110) d'isolation de contraintes monté à l'intérieur de la première ouverture
(112) du support (122), l'élément (110) d'isolation de contraintes présentant une
forme de parallélépipède rectangle et définissant une deuxième ouverture (108) s'étendant
longitudinalement à travers la forme de parallélépipède rectangle, l'élément (110)
d'isolation de contraintes étant composé de silicium, et la section droite de la première
ouverture correspondant à une section droite extérieure de l'élément d'isolation de
contraintes ; et
une pastille (106) de capteur collée à l'élément (110) d'isolation de contraintes,
la pastille (106) de capteur comprenant :
un substrat en silicium doté d'une couche d'isolant sur un premier côté (105) du substrat
en silicium ; et
une circuiterie de détection disposée dans la couche d'isolant sur le premier côté
(105), un deuxième côté (107) du substrat en silicium étant exposé à la deuxième ouverture
(108) de l'élément (110) d'isolation de contraintes et le deuxième côté (107) étant
à l'opposé du premier côté (105) ; et le deuxième côté du substrat en silicium étant
collé à une première surface de l'élément d'isolation de contraintes pour former un
liaison silicium-silicium entre la pastille de capteur et l'élément d'isolation de
contraintes,
l'élément (110) d'isolation de contraintes s'éloignant du deuxième côté (107) du substrat
en silicium, la pastille (106) de capteur étant montée sur une première extrémité
de l'élément (110) d'isolation de contraintes, le support (122) étant monté à proximité
d'une deuxième extrémité (114) de l'élément (110) d'isolation de contraintes, la deuxième
extrémité (114) étant à l'opposé de la première extrémité.
2. Capteur (100) de pression selon la revendication 1, le support (122) étant réalisé
à partir d'une céramique.
3. Capteur (100) de pression selon la revendication 1 ou 2, comportant en outre un revêtement
(126) par dépôt en couche atomique qui recouvre une surface intérieure de l'élément
(110) d'isolation de contraintes et du deuxième côté (107) du substrat en silicium
qui sont exposés au milieu.
4. Capteur (100) de pression selon la revendication 3, le revêtement (126) par dépôt
en couche atomique recouvrant une partie du support (122).
5. Capteur (100) de pression selon l'une quelconque des revendications 1 à 4, le support
(122) et l'élément (110) d'isolation de contraintes étant assemblés à l'aide d'une
brasure (116).
6. Capteur (100) de pression selon l'une quelconque des revendications 1 à 5, une orientation
cristalline de l'élément (110) d'isolation de contraintes étant alignée avec une orientation
cristalline de la pastille (106) de capteur.
7. Procédé (300) de réalisation d'un capteur de pression, le procédé comportant les étapes
consistant à :
réaliser des ensembles multiples de piézo-résistances (302) dans une couche d'isolant
d'une première tranche de silicium, chaque ensemble de piézo-résistances correspondant
à une circuiterie de détection pour une pastille de capteur ;
graver une pluralité de trous débouchants (304) dans une deuxième tranche de silicium,
chaque trou débouchant correspondant à une première ouverture pour un élément d'isolation
de contraintes ;
coller la deuxième tranche de silicium (306) à un côté de la première tranche de silicium
opposé à la couche d'isolant en utilisant un processus de diffusion silicium-silicium,
de surface à surface, à basse température, le collage comprenant l'alignement de la
deuxième tranche de silicium avec la première tranche de silicium de telle façon que
chaque trou débouchant soit à l'opposé d'un ensemble de piézo-résistances ;
découper en dés les première et deuxième tranches (310) de silicium collées pour former
une pluralité de primitives discrètes de capteur de pression, chaque primitive de
capteur de pression comprenant :
une pastille de capteur collée à un élément d'isolation de contraintes, la pastille
de capteur étant composée d'une partie de la première tranche de silicium comprenant
un ensemble de piézo-résistances ; et
l'élément d'isolation de contraintes composé d'une partie de la deuxième tranche de
silicium, l'élément d'isolation de contraintes présentant une forme de parallélépipède
rectangle et définissant la première ouverture (108) s'étendant longitudinalement
à travers la forme de parallélépipède rectangle ;
mettre en place une pluralité de supports, chaque support définissant une deuxième
ouverture présentant une section droite uniforme s'étendant à travers le support,
et la section droite de la deuxième ouverture correspondant à une section droite extérieure
de l'élément d'isolation de contraintes ;
monter chaque primitive de capteur de pression sur un support (312) de telle façon
qu'une partie de la surface extérieure de chaque élément d'isolation de contraintes
soit fixée à la surface intérieure de la deuxième ouverture d'un support correspondant,
le montage de chaque primitive de capteur de pression sur un support comprenant le
brasage du dispositif de capteur de pression sur le support, chaque primitive de capteur
de pression étant montée de telle façon que le support soit brasé sur l'élément d'isolation
de contraintes à proximité d'une extrémité de l'élément d'isolation de contraintes
qui est à l'opposé d'une extrémité dans laquelle est montée la pastille de capteur
;
monter l'élément d'isolation de contraintes d'une primitive de capteur de pression
sur un boîtier (314) ;
revêtir les surfaces de l'élément d'isolation de contraintes et de la pastille de
capteur appelées à être exposées à un milieu par un dépôt en couche atomique d'un
oxyde métallique ; et
étanchéifier le boîtier (318) de telle façon que le côté de la pastille de capteur
doté de la circuiterie de détection soit à l'intérieur d'un environnement présentant
une pression connue et soit hermétiquement isolé de la deuxième ouverture de l'élément
d'isolation de contraintes.
8. Procédé selon la revendication 7, comportant les étapes consistant :
après avoir collé la deuxième tranche de silicium à la première tranche de silicium,
à réaliser des tracés métalliques et des plages (308) de connexion de fils sur un
côté de la première tranche de silicium doté de la couche d'isolant pour former une
circuiterie de détection.
9. Procédé selon l'une quelconque des revendications 7 et 8, le collage comprenant un
collage à moins de 600 degrés Celsius.
10. Capteur (100) de pression selon l'une quelconque des revendications 1 à 6, l'élément
(110) d'isolation de contraintes présentant les mêmes dimensions en section droite
que la pastille (106) de capteur.